Powder metallurgical manufacturing techniques are generally characterized by long series production of components having good dimensional accuracy. The manufacturing sequence is generally started by mixing a metallic powder with a lubricant in order to simplify a subsequent compression operation. The metallic powder may e.g. be a powder formed of pre-alloyed atomised particles, a powder admixed with alloying elements in powder form, or a powder wherein alloying elements are diffusion-alloyed or diffusion-bonded to a metal base powder. The compacted (green) component is then heated and is retained at a temperature, at which the green component obtains, by means of sintering, its final characteristics with regard to strength, ductility etc.
Bronze powder is commonly used in production of sintered self-lubricating bearings. The use of bronze will give the bearing favourable characteristics such as quiet running and good wear resistance, bronze is also less prone to corrosion. In order to reduce the costs however iron powder is added for production of so called diluted bronze bearings. It is common to use about 40-60% by weight of iron powder. The bearings often replace bronze bearings in fractional horse power motors and applications.
Diffusion-bonded powders are known from several publications. In the GB patent 1162702 (1965) a process for preparing a powder is disclosed. In this process alloying elements are diffusion-bonded (partially alloyed) to the iron powder particles. An unalloyed iron powder is heated together with alloying elements, such as copper and molybdenum, in a reducing atmosphere at a temperature below the melting point to cause pre-alloying and agglomeration of the particles. The heating is discontinued before complete alloying and the obtained agglomerate is ground to a desired size. Also the GB patent 1595346 (1976) discloses a diffusion-bonded powder. The powder is prepared from a mixture of an iron powder and a powder of copper or easily reducible copper compounds. The obtained powder wherein copper is diffusion-bonded to the iron powder is distinguished by high compressibility and low risk of segregation and dusting.
A different technology of providing copper on atomised powder particles is disclosed in JP 59-050101 (1982) which concerns an atomized iron powder containing at least 0.05% by weight of tin. This powder is then coated with a copper layer.